Solenoid transient variable resistance feedback for effecter position detection

ABSTRACT

Feedback from a solenoid is achieved by adding at least one variable resistance in parallel with the solenoid current feedback circuit for position detection. The resistance has current flowing therethrough when a switching device actuated by the solenoid is in one position or transitions from one position to at least one other position. A feedback current may be measured in the current feedback circuit and the position of the switching device in response to actuation thereof by the solenoid may be determined from the measured feedback current.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/554,134, filed on Jul. 20, 2012, the contents of which arehereby incorporated by reference in their entirety.

TECHNICAL FIELD

The application relates generally to a system and method for detectingthe position of a switching device actuated by a solenoid.

BACKGROUND OF THE ART

Solenoids may be used to actuate switching devices in a variety ofapplications, such as fuel transmission systems or vehicle brakesystems. As the response of the switching device to the actuationcommand of the solenoid may be of primary importance for a givenapplication, it is desirable to monitor the operation of the solenoidand of the switching device. For this purpose, a variety of externalsensing devices may be used to detect electrical or mechanical faultspreventing operation of the solenoid or to provide feedback as towhether the switching device has operated as commanded by the solenoid.However, the use of such devices typically increases the weight,complexity and cost of the overall system.

There is therefore a need for an improved system and method fordetecting the position of a switching device actuated by a solenoid.

SUMMARY

In one aspect, there is provided a switching device position detectionsystem comprising a solenoid adapted to generate mechanical energy froman energizing current supplied thereto; a switching device coupled tothe solenoid and adapted to be driven by the mechanical energy to movebetween a first position and at least one second position; at least onemeasuring element coupled to the switching device, the at least onemeasuring element adapted to be engaged by the switching device and tohave a measuring current flowing therethrough when the switching devicemoves to the at least one second position; and a solenoid driver coupledto the solenoid and to the at least one measuring element and adapted tosupply the energizing current to the solenoid and to detect themeasuring current to determine whether the switching device has moved tothe at least one second position.

In another aspect, there is provided a switching device positiondetection method comprising energizing a solenoid by supplying anenergizing current from a solenoid driver coupled thereto, therebyactuating a switching device coupled to the solenoid to move between afirst position and at least one second position; generating a measuringcurrent through at least one measuring element coupled to the switchingdevice when the switching device moves between the first position andthe at least one second position; and detecting the measuring current atthe solenoid driver to determine whether the switching device has movedto the at least one second position.

In a further aspect, there is provided a switching device positiondetection system comprising means for energizing a solenoid by supplyingan energizing current from a solenoid driver coupled thereto, therebyactuating a switching device coupled to the solenoid to move between afirst position and at least one second position; means for generating ameasuring current through at least one measuring element coupled to theswitching device when the switching device moves between the firstposition and the at least one second position; and means for detectingthe measuring current at the solenoid driver to determine whether theswitching device has moved to the at least one second position; andmeans for determining whether the switching device has moved to the atleast one second position.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1 is a schematic side cross-sectional view of a gas turbine engine;

FIG. 2a is a schematic diagram of a switching device position detectionsystem in accordance with a first illustrative embodiment;

FIG. 2b is a schematic diagram of the switching device positiondetection system of FIG. 2a comprising a switch and a resistor;

FIG. 3 is a schematic diagram of an exemplary embodiment of the solenoiddriver of FIG. 2 a;

FIG. 4 is a schematic diagram of a position detection system for amulti-position switching device in accordance with a second illustrativeembodiment;

FIG. 5 is a schematic diagram of a position detection system for amulti-position switching device adapted to pass through a transientposition in accordance with a third illustrative embodiment;

FIG. 6 is a graph of an exemplary transient current profile of thesolenoid of FIG. 5;

FIG. 7 is a schematic diagram of a position detection system for amulti-position switching device adapted to pass through a plurality oftransient positions in accordance with a fourth illustrative embodiment;and

FIG. 8 is a flowchart of a method for detecting the position of aswitching device in accordance with an illustrative embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a gas turbine engine 10 of a type typically providedfor use in subsonic flight, generally comprising in serial flowcommunication a fan 12 through which ambient air is propelled, acompressor section 14 for pressurizing the air, a combustor 16 in whichthe compressed air is mixed with fuel and ignited for generating anannular stream of hot combustion gases, and a turbine section 18 forextracting energy from the combustion gases. High pressure rotor(s) 20of the turbine section 18 are drivingly engaged to high pressurerotor(s) 22 of the compressor section 14 through a high pressure shaft24. Low pressure rotor(s) 26 of the turbine section 18 are drivinglyengaged to the fan rotor 12 and to other low pressure rotor(s) 28 of thecompressor section 14 through a low pressure shaft 30 extending withinthe high pressure shaft 24 and rotating independently therefrom.

Referring to FIG. 2a and FIG. 2b , the engine 10 may comprise aplurality of switching devices 32, such as two-way switching valves,bypass valves, proportional valves, switches, or the like, used forcontrolling an operation thereof. For example, such switching devices 32may include valves (not shown) used as part of a fuel system forenabling fuel, such as diesel oil pressurized by a suitable pump, toflow into the engine 10. During the starting of the gas turbine engine10, the valve may be opened so that a portion of the fuel may flowthrough a starter manifold to combustion equipment (not shown) for theinitiation of combustion. As soon as combustion has been initiated andsustained, the valve may be closed so that all the fuel may pass througha main manifold to burners. Still, it should be understood that theswitching devices 32 may be used in applications other than fuel controlsystems, such as in engine health monitoring systems.

The switching device 32 may be driven by a solenoid 34 coupled to asolenoid driver 36, such as a microprocessor having preprogrammed logic(not shown). As illustrated in FIG. 2b , the solenoid 34 may comprise acoil 38 wrapped around a movable plunger 40 normally occupying a firstphysical position and displaced to a second physical position when thecoil 38 is energized. For this purpose, the solenoid driver 36, whichmay be coupled to a power source (not shown), may generate a currentcommand I_(C) and send the current command I_(C) to the solenoid 34 forsupplying electrical energy to the coil 38. As a result, a current I_(S)may flow through the solenoid 34, thereby energizing the coil 38 andgenerating mechanical energy to displace the plunger 40 from the firstposition to the second position. The solenoid driver 36 may use avariety of methods for directing the current command I_(C) to thesolenoid 34. For example, a constant electrical current may be turned onor off according to a desired position to be achieved by the solenoid34. A pulse width modulation electrical current may also be used, withthe pulse width modulations being set at a predetermined frequency sothat the solenoid 34 may be activated and deactivated at desired timeperiods.

The movable plunger 40 of the solenoid 34 is illustratively connected tocontacts of the switching device 32, such that the movement of themovable plunger 40 through the coil 38 actuates the switching device 32.When actuated, the switching device 32 may then move between at least afirst, e.g. open, position A and a second, e.g. closed, position B. Morepositions may be provided depending on whether the switching device 32is a single-position or a multi-position switching device, as will bediscussed below.

A current feedback I_(F), equal to the sum of the current I_(S) flowingthrough the solenoid 34 and the current, if any, flowing through theswitching device 32, may be measured by a suitable sensor (not shown)and received at the solenoid driver 36 for monitoring the state of thesolenoid 34 and of the switching device 32. On the basis of the value ofsuch a current feedback I_(F), the solenoid driver 40 may adjust themagnitude of a new solenoid current command I_(C) generated to sustainthe energization of the coil 38 or alternatively de-energize the coil 38if a desired operation, e.g. opening or closing of the switching device32, has been fully achieved. For instance, the solenoid driver 36 maymeasure the current feedback I_(F) and compare the current feedbackI_(F) to a threshold predetermined according to the physicalcharacteristics of the solenoid 34 and the switching device 32. If thecurrent feedback I_(F) is below the threshold, the solenoid driver 36may generate a current command I_(C) that keeps the coil 38 energized.In this manner, the current I_(S) flowing through the solenoid 34, andthereby the operation of the solenoid 34, may be regulated in a closedloop fashion by the solenoid driver 36.

In order to monitor the operation of the switching device 32 andtherefore detect potential faults, a sensing or measuring element 42,such as a resistor as illustrated in FIG. 2b , may be placed in parallelwith the solenoid current feedback circuit comprising the solenoid 34and the solenoid driver 36. It should be understood that although thedescription refers to a resistor 42, any other suitable measuringelement known to those skilled in the art may be coupled to theswitching device 32 to monitor a position thereof. When the switchingdevice 32 is in the first, i.e. open, position A, no current may flowtherethrough and the current feedback I_(F) entering the solenoid driver36 equals the current I_(S) flowing through the solenoid 34, with thecurrent I_(S) flowing through the solenoid 34 being illustratively equalto the current command I_(C) previously sent by the solenoid driver 36to the solenoid 34 to actuate the solenoid 34. Measurements made whilethe switching device 32 is in position A correspond to time t=t₁. Whenthe switching device 32 moves to the second, i.e. closed, position Bshown in dotted line, the switching device 32 engages the resistor 42.This results in a current I_(R) flowing through the resistor 42 as longas the switching device 32 remains in the second position B, and thus inan increase in the solenoid current feedback I_(F) at a time t=t₂compared to the previously measured I_(F) at time t=t₁.

Referring to FIG. 3, the current increase I_(R) may be detected by thesolenoid driver 36, which monitors the current feedback I_(F). For thispurpose, the solenoid driver 36 may comprise a comparison module 44, aposition detection module 46, and a command generation module 48. Thecomparison module 44 is illustratively adapted to receive the reading ofthe current feedback I_(F) and compare the reading to the predeterminedthreshold, such as the current command I_(C) at time t=t₁. The result ofthe comparison may then be sent to the position detection module 46,which may be adapted to determine the position of the switching device32 according to the comparison. Indeed, if the received reading of thecurrent feedback I_(F) at time t=t₂ is equal to the previously issuedcurrent command I_(C) at time t=t₁, the solenoid driver 36 may determinethat the switching device 32 is in the first position A. Alternatively,if the reading at time t=t₂ is greater than the previously issuedcurrent command I_(C) at time t=t₁ by a value equal to the value of thecurrent increase I_(R), which may be retrieved from a database (notshown) coupled to the solenoid driver 36, the current increase I_(R) maybe detected. The resistive value of the resistor 42 may indeed be storedin the database and retrieved by the solenoid driver 36 to determine acorresponding value of the current increase I_(R). As a result, thesolenoid driver 36 may detect that the switching device 32 has moved tothe second position B.

The position detection module 46 may then send the position estimate tothe command generation module 48, which may generate a new currentcommand I_(C) to be sent to the solenoid 34 for controlling a movementof the plunger 40 relatively to the coil 38 and therefore adjust aposition of the switching device 32. For example, if the positionestimate indicates that the switching device 32 is in position A whileit is desired to move the switching device 32 to position B, the valueof the current command I_(C) may be adjusted accordingly so that thesolenoid 34 may remain energized and further actuate the switchingdevice 32 to the desired position.

Referring to FIG. 4, according to an alternate embodiment, the switchingdevice 32 may be adapted to move among a plurality of closed positions,e.g. two positions A, B. Accordingly, a plurality of resistors, e.g. tworesistors 42 ₁, 42 ₂, having different resistive values may be providedin the solenoid current feedback circuit, with each resistor 42 ₁, 42 ₂adapted to be engaged by the switching device 32 when the switchingdevice 32 is in a given closed position A, B. For example, the switchingdevice 32 may be adapted to move between a first closed position A and asecond closed position B and, as such, a first resistor 42 ₁ and asecond resistor 42 ₂ may be respectively provided for each position A,B. In this manner, when in the position A, the multi-position switchingdevice 32 may engage the first resistor 42 ₁, thus leading to a currentI_(R), flowing therethrough as long as the switching device 32 remainsin position A. When the multi-position switching device 32 moves to theposition B, the resistor 42 ₂ may be engaged, thus leading to a currentI_(R2) flowing therethrough as long as the switching device 32 remainsin position B. The current I_(R1) or I_(R2) flowing through eitherresistor 42 ₁ or 42 ₂ engaged by the switching device 32 may then add tothe current I_(S) (equal to the previously issued current command I_(C))flowing through the solenoid 34 to form the current feedback I_(F) sentto the solenoid driver 36.

In order to identify the resistor 42 ₁ or 42 ₂, which has been engagedby the switching device 32, and accordingly the position thereof, thecurrent increase I_(R1), or I_(R2) may be detected by the solenoiddriver 36 using the comparison module 44 to compare the reading of thecurrent feedback I_(F) at time t=t₂ to the previously issued currentcommand I_(C) at time t=t₁. In particular, if the result of thecomparison indicates that the current feedback I_(F) at time t=t₂ isgreater than the previously issued current command I_(C) at time t=t₁ bya value of I_(R1), the position detection module 46 may determine thatthe resistor 42 ₁ has been engaged by the switching device 32 and thatthe switching device 32 is therefore in position A. If the result of thecomparison indicates that the current feedback I_(F) at time t=t₂ isgreater than the previously issued current command I_(C) at time t=t₁ bya value of I_(R2), the position detection module 46 may identify thatthe resistor 42 ₂ has been engaged by the switching device 32 and thatthe switching device 32 is therefore in position B. If no resistor 42 ₁or 42 ₂ has been engaged, no current increase I_(R1) or I_(R2) willillustratively be detected and the position of the switching device 32,i.e. the open position (not shown), will be determined accordingly.

Referring to FIG. 5, according to an alternative embodiment, theswitching device 32 may be adapted to pass through a transient positionT when moving between a first steady state position A and a secondsteady state position B. Accordingly, a resistor 50 may be coupled tothe switching device 32 and adapted to be temporarily engaged by theswitching device 32 when the switching device 32 passes through thetransient position T. When the resistor 50 is engaged, a current I_(T)may flow through the resistor 50, resulting in a momentary current spikein the current feedback I_(F) monitored by the solenoid driver 36. Thus,the solenoid driver 36 may identify the current spike I_(T) as beingrepresentative of the switching device 32 transitioning from the firstposition A to the second position B, and vice versa. According to themonitored current feedback I_(F), the solenoid driver 36 may thereforedetermine the position of the switching device 32.

FIG. 6 shows the transient current profile of the current feedback I_(F)versus time as the solenoid 34 moves between steady state positions Aand B. At time 0, the solenoid 34 is illustratively energized. From time0 to time 1, the current profile thus increases until a steady statecurrent I_(SS) is reached when the switching device is in steady stateposition A. An inflection point X may occur in the current profile dueto a back electro-motive force generated by the movement of the plunger40 through the coil 38. At time 1, the switching device 32 may move fromposition A to position B by passing through the transient position T, inwhich the resistor 50 is temporarily engaged. As a result, the currentspike I_(T) occurs and the current feedback I_(F) reaches a peak valueI_(PEAK). At time 2, the switching device 32 may move out of thetransient position T towards the steady state position B. The resistor50 is therefore no longer engaged and the current feedback I_(F)decreases to eventually reach the steady state value I_(SS) when theswitching device 32 is in steady state position B.

In this embodiment, the solenoid driver 36 may receive at the comparisonmodule 44 a reading of the current feedback I_(F) and identify amomentary peak current I_(PEAK) during the transition of the solenoid 34from position A to position B, or vice versa. The comparison module 44may then compare the peak current I_(PEAK) to a predetermined thresholdor current feedback trip point I_(TRIP). The current feedback trip pointI_(TRIP) may be set to a value greater than the value of the currentcommand I_(C) in order to take into account the increase in resistance,and in turn the increase in current I_(S) flowing through the solenoid34, as the solenoid 34 ages regardless of the current command I_(C)supplied thereto. If the peak current I_(PEAK) is equal to or greaterthan the current feedback trip point I_(TRIP), the comparison module 44may determine that the current spike I_(T) has occurred and the positiondetection module 46 may identify, on the basis of the comparison, thatthe switching device 32 has successfully moved positions. Otherwise, itmay be determined that no current spike has occurred and that theswitching device 32 has not moved positions despite a current commandI_(C) having been previously sent by the command generation module 48 tothe solenoid 34 for energizing the solenoid 34. The position detectionmodule 46 may therefore identify that a fault has occurred.

Referring to FIG. 7, the switching device 32 may be adapted to moveamong a plurality of steady state positions, as in A, B, and C, bypassing through one of a plurality of transient positions, as in T1 andT2, when transitioning between a pair of the steady state positions. Assuch, a plurality of resistors, as in 50 ₁, 50 ₂, having differentresistive values may be coupled to the transient positions T1, T2 andeach adapted to be engaged by the switching device 32 when the switchingdevice 32 passes through the corresponding transient position T1 or T2.For example, if the switching device 32 moves from the first steadystate position A to the second steady state position B, the switchingdevice 32 may pass through the first transient position T1 andtemporarily engage the first resistor 50 ₁. As a result, a first currentspike I_(T1) may occur. At this point, the first expected value of thecurrent feedback I_(F) is illustratively equal to the sum of thesolenoid current I_(S), which is also equal to the previously issuedcurrent command I_(C), and the first current spike I_(T1). When theswitching device 32 moves from the second steady state position B to thethird steady state position C and passes through the second transientposition T2, the switching device 32 may temporarily engage the secondresistor 50 ₂, thus resulting in a second current spike I_(T2). In thiscase, the second expected value of the current feedback I_(F) is equalto the sum of the previously issued current command I_(C) and the secondcurrent spike I_(T2).

At any point during the transition of the switching device 32 from oneposition A, B, C to the next, the comparison module 44 may receive areading of the current feedback I_(F) and identify the peak valueI_(PEAK) of the current feedback I_(F). The comparison module 44 maythen correlate the peak value I_(PEAK) to the expected value of thecurrent feedback I_(F). For instance, the comparison module 44 maydetermine that the peak value I_(PEAK) is lower than either the first orthe second expected value of the current feedback I_(F) described above.The position detection module 46 may therefore identify that theswitching device 32 has not passed through either transient position T1or T2. In particular, assuming that the resistive value of the resistors50 ₁, 50 ₂ is selected such that the first current spike I_(T1) issmaller than the second current spike I_(T2), if the peak value I_(PEAK)is smaller than the first expected value of the current feedback I_(F),the position detection module 46 may detect that the switching devicehas not passed through transient position T1 and is therefore still inposition A. If the peak value I_(PEAK) is equal to or greater than thefirst expected value yet smaller than the second expected value, theposition detection module 46 may identify that the switching device 32has passed through the first transient position T1 but not through thesecond transient position T2 and is therefore in position B. If the peakvalue I_(PEAK) is equal to or greater than the second expected value,the position detection module 46 may identify that the switching device32 has passed through the second transient position T2 and is thereforein position C. Adjusting the resistive value of the resistors 50 ₁, 50 ₂may allow to vary the current ranges used to determine the physicalposition of the driven switching device 32.

Feedback of the position of the switching device 32, and accordinglyfault detection, may therefore be provided using the driving circuit ofthe solenoid 34 and without the need for discrete inputs to be receivedfrom an external sensing device, such as a discrete switch, temperaturesensor, pressure sensor, Linear Variable Differential Transformer(LVDT), or the like, which may be coupled to the switching device 32. Inaddition, when the switching device 32 is in steady state operation,e.g. in position A, B, or C of FIG. 6, no added power consumptionillustratively results from the presence of the resistors 50 ₁, 50 ₂ inthe current feedback circuit. Thus, it may be possible to determinewhether the switching device 32 has operated in response to the movementof the solenoid 34 using circuitry having reduced weight, cost, andcomplexity.

Referring to FIG. 8, a method 200 for detecting the position of aswitching device 32 will now be described. The method 200 comprises atstep 202 receiving the reading of the current feedback I_(F). Once thereading is received, the reading of the current feedback I_(F) may becompared (step 204) to a predetermined threshold, such as the currentcommand I_(C) previously sent to the solenoid 34, the current feedbacktrip point I_(TRIP), or the expected value of the current feedbackI_(F), as discussed above. The next step 206 is then to infer theposition of the switching device 32 according to the result of thecomparison. For example, in the case illustrated in FIG. 2a where asingle resistor 42 may be engaged by the single position switch 32, ifthe current feedback I_(F) is equal to the current command I_(C), it maybe determined that the switching device 32 is in position A. Once theposition of the switching device 32 has been inferred, a new solenoidcurrent command I_(C) may be generated to control the energizationlevel, and therefore the operation, of the solenoid 34 so that theswitching device 32 may be placed in a desired position.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.Modifications which fall within the scope of the present invention willbe apparent to those skilled in the art, in light of a review of thisdisclosure, and such modifications are intended to fall within theappended claims.

The invention claimed is:
 1. A switching device position detectionsystem comprising: a solenoid adapted to generate mechanical energy froman energizing current supplied thereto; a switching device coupled tothe solenoid and adapted to be driven by the mechanical energy generatedfrom the solenoid to move between a first position and at least onesecond position; at least one measuring element coupled to the switchingdevice, the at least one measuring element adapted to be engaged by theswitching device and to have a measuring current flowing therethroughwhen the switching device moves to the at least one second position; anda solenoid driver coupled to the solenoid to supply the energizingcurrent to the solenoid, the solenoid driver coupled to the at least onemeasuring element to detect the measuring current and configured toidentify a fault in the switching device when the energizing current hasbeen supplied to the solenoid and the measuring current is not detectedby the solenoid driver.
 2. The system of claim 1, wherein the solenoiddriver is adapted to update the energizing current for supply to thesolenoid.
 3. The system of claim 1, wherein the solenoid driver isadapted to receive a feedback current comprising a sum of the energizingcurrent and the measuring current when the at least one measuringelement has moved to the at least one second position, and compare thefeedback current to a predetermined threshold to detect the measuringcurrent.
 4. The system of claim 3, wherein the predetermined thresholdcorresponds to the energizing current at a time t=t₁ preceding a timet=t₂ at which the switching device has moved to the at least one secondposition.
 5. The system of claim 1, wherein the at least one measuringelement comprises at least one resistor.
 6. The system of claim 1,wherein the switching device is adapted to move between the firstposition and a plurality of successive second positions.
 7. The systemof claim 6, wherein the at least one measuring element comprises a firstmeasuring element, the first measuring element adapted to be engaged bythe switching device and to have a first measuring current flowingtherethrough when the switching device is in the first position, and aplurality of second measuring elements each adapted to be successivelyengaged by the switching device and to have a second measuring currentflowing therethrough when the switching device is in a corresponding oneof the plurality of successive second positions.
 8. The system of claim7, wherein the second measuring current flowing through a first one ofthe plurality of second measuring elements is different from the firstmeasuring current and from the second measuring current flowing througha second one of the plurality of second measuring elements.
 9. Thesystem of claim 1, wherein the switching device is adapted to movebetween a plurality of successive steady state positions and to passthrough a transient position when moving between each pair of theplurality of successive steady state positions.
 10. The system of claim9, wherein the at least one measuring element comprises a plurality ofmeasuring elements each adapted to be temporarily engaged by theswitching device and have the measuring current flowing therethroughwhen the switching device passes through the transient position.
 11. Aswitching device position detection method comprising: energizing asolenoid by supplying an energizing current from a solenoid drivercoupled thereto, thereby actuating a switching device coupled to thesolenoid to move between a first position and at least one secondposition when the solenoid generates mechanical energy in response tobeing energized; generating a measuring current through at least onemeasuring element coupled to the switching device when the switchingdevice moves between the first position and the at least one secondposition; detecting the measuring current from the measuring element atthe solenoid driver; and identifying a fault in the switching devicewhen the energizing current has been supplied to the solenoid and themeasuring current is not detected by the solenoid driver.
 12. The methodof claim 11, wherein detecting the measuring current comprises receivinga feedback current comprising a sum of the energizing current and themeasuring current when the at least one measuring element has moved tothe at least one second position, and comparing the feedback current toa predetermined threshold.
 13. The method of claim 12, wherein comparingthe feedback current to a predetermined threshold comprises comparingthe feedback current to the energizing current at a time t=t₁ precedinga time t=t₂ at which the switching device has moved to the at least onesecond position.
 14. The method of claim 11, further comprising updatingthe energizing current for supply to the solenoid.
 15. The method ofclaim 11, wherein energizing the solenoid actuates the switching deviceto move between the first position and a plurality of successive secondpositions.
 16. The method of claim 15, wherein generating a measuringcurrent comprises generating the measuring current through a firstmeasuring element coupled to the switching device when the switchingdevice is in the first position and generating the measuring currentthrough each one of a plurality of second measuring elements coupled tothe switching device when the switching device is in a corresponding oneof the plurality of successive second positions.
 17. The method of claim11, wherein energizing the solenoid actuates the switching device tomove between a plurality of successive steady state positions and topass through a transient position when moving between each pair of theplurality of successive steady state positions.
 18. The method of claim17, wherein generating a measuring current comprises generating themeasuring current through each one of a plurality of measuring elementscoupled to the switching device when the switching device passes throughthe transient position.
 19. A switching device position detection systemcomprising: means for energizing a solenoid by supplying an energizingcurrent from a solenoid driver coupled thereto, thereby actuating aswitching device coupled to the solenoid to move between a firstposition and at least one second position when the solenoid generatesmechanical energy in response to being energized; means for generating ameasuring current through at least one measuring element coupled to theswitching device when the switching device moves between the firstposition and the at least one second position; and means for detectingthe measuring current from the measuring element at the solenoid driver;and means for identifying a fault in the switching device when theenergizing current has been supplied to the solenoid and the measuringcurrent is not detected by the solenoid driver.